The present invention relates to a cleaning module for the cleaning of components of an EUV lithography device comprising a heating unit, and to a cleaning module for an EUV lithography device with a supply line for molecular hydrogen and a heating filament for producing atomic hydrogen for cleaning purposes, as well as to an EUV lithography device or a projection system or an illumination system for an EUV lithography device with such a cleaning module. Moreover, the present invention relates to methods for the cleaning of a component inside an EUV lithography device.
In extreme-ultraviolet lithography devices, reflective optical elements for the extreme ultraviolet (EUV) or soft x-ray wavelength range (e.g. wavelengths between approx. 5 nm and 20 nm), such as for example photomasks and multilayer mirrors, are used for the lithography of semiconductor components. Since EUV lithography devices usually comprise a plurality of reflective optical elements, these elements must possess as high a reflectivity as possible in order to ensure a sufficiently high total reflectivity. The reflectivity and the service life of the reflective optical elements can be reduced by contamination of the optically used reflective area of the reflective optical elements, said contamination arising on account of the shortwave radiation together with residual gases in the operating atmosphere. Since a plurality of reflective optical elements are usually arranged behind one another in an EUV lithography device, even fairly small levels of contamination on each individual reflective optical element have a quite considerable effect on the total reflectivity.
In particular, the optical elements of an EUV lithography device can be cleaned in situ with the aid of, for example, atomic hydrogen, which reacts with, in particular, carbon-containing contamination to form volatile compounds. In order to obtain the atomic hydrogen, molecular hydrogen is often conveyed onto a heating filament. Metals or metal alloys with a particularly high melting point are used for the heating filament. So-called cleaning heads comprising a hydrogen supply line and an incandescent filament are arranged in the vicinity of mirror surfaces in order to clean them free from contamination. The volatile compounds, which are formed in the reaction of the atomic hydrogen with the, in particular, carbon-containing contamination, are pumped away with the normal vacuum system.
It has been a problem with the previous approach that, on the one hand, the cleaning heads are supposed to be arranged relatively close to the mirrors in order to achieve a high cleaning efficiency. On the other hand, reflective optical elements optimized precisely for the EUV or soft x-ray wavelength region are often sensitive to heat. Excessive heating of the mirrors during the cleaning leads to a deterioration in their optical properties. Hitherto, therefore, mirror cooling has been provided during the cleaning or the cleaning has been carried out as pulsed cleaning with cooling phases. Furthermore, with the production of atomic hydrogen via thermionic electrons from, for example, an incandescent or heating filament, the problem arises that the filament material can contaminate the surface to be cleaned.